JP3736796B2 - Wavelength detection device and fluorine molecular laser device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wavelength detection device and a fluorine molecular laser device using the same, and more particularly to a wavelength detection device for accurately controlling the emission wavelength of a fluorine molecular laser device for a semiconductor exposure apparatus and a fluorine molecular laser equipped with the wavelength detection device. It relates to the device.
[0002]
[Prior art]
In an exposure technique for realizing a semiconductor integrated circuit having a line width of 70 nm or less on a semiconductor, an exposure light source having a wavelength of 160 nm or less is required. Currently, F that emits ultraviolet light having a wavelength of about 157 nm is emitted.₂A (fluorine molecule) laser device is regarded as a promising light source.
[0003]
F₂As shown in FIG. 13, the laser device has two main oscillation wavelengths (λ₁= 157.6299nm, λ₂= 157.5233 nm: Sov. J. Quantum Electron. 16 (5), May 1986), and its spectral line width (FWHM: full width at half maximum) is about 1 pm. The intensity ratio I (λ of the two oscillation lines₁) / I (λ₂) Is about 7. Usually, the wavelength λ is strong for exposure.₁(= 157.6299 nm) oscillation line is used.
[0004]
By the way, there are the following two types of semiconductor exposure techniques.
[0005]
1) Using a dioptric system
2) Using a catadioptric system
When the catadioptric optical system is used for the exposure technique, since the reflective optical element has no chromatic dispersion, the occurrence of chromatic aberration can be suppressed by combining the reflective optical element and the refractive optical element. Therefore, an exposure apparatus using a catadioptric system is promising in the present wavelength range near 157 nm. However, the catadioptric system is difficult to adjust the optical axis of the exposure machine as compared with the conventional refractive system, and is difficult to mass-produce.
[0006]
On the other hand, the refractive system is a projection optical system that is generally used in a conventional semiconductor exposure apparatus. In the semiconductor exposure technology, the chromatic aberration correction method in the optical system is one big problem. In the refraction system, chromatic aberration correction has been realized by combining optical elements such as lenses having different refractive indexes. However, there is a limit to the types of optical materials that can be used in the wavelength region near 157 nm, and currently CaF₂It is in the situation which cannot be used except.
[0007]
Therefore, F as a light source for a refractive exposure apparatus.₂A narrow band is required for the laser device. Specifically, it is required to narrow the full width at half maximum of the laser beam spectrum to 0.3 pm or less. In this case, it is necessary to install a band narrowing element for narrowing the band in the laser resonator.
[0008]
Further, F as a light source of a catadioptric exposure apparatus.₂The laser device does not require a narrow band, but as described above, F₂Since the laser device has two main oscillation wavelengths, the stronger wavelength λ₁It is necessary to select an oscillation line (= 157.6299 nm) (line select method).
[0009]
By the way, it is necessary to perform stabilization control with high accuracy so that the center wavelength of the spectrum of the oscillation laser beam does not shift during exposure. For this purpose, the relative wavelength of the oscillation laser light with respect to the reference light is always detected in the monitor module during exposure to detect the absolute wavelength of the oscillation laser light. In the case of a narrow band laser apparatus, the center wavelength is stabilized by feeding back the detection result to the laser wavelength controller and driving the narrow band element. In the case of a line select laser device, the center wavelength of the spectrum of the oscillation laser light is stabilized by controlling the laser gas pressure in the laser chamber.
[0010]
Conventionally, in Japanese Patent Laid-Open No. 2000-249600, F₂A reference light of a wavelength detection device that detects the wavelength of a laser device and a wavelength detection device thereof have been proposed.
[0011]
Japanese Patent Laid-Open No. 2000-162047 calculates the wavelength of the detected light (ArF excimer laser light, KrF excimer laser light) by calculating the known two reference lights and their positions and correcting the dispersion value of the spectrometer. There has been proposed a wavelength detection device that calculates the above.
[0012]
[Problems to be solved by the invention]
However, as disclosed in Japanese Patent Laid-Open No. 2000-249600, it is known that the spectrum shape of an emission line used as reference light has various shapes when using one or more emission lines as reference light. For example, F₂For bromine (Br) having an emission line closest to the wavelength of the laser, as shown schematically in FIG. 14A, the spectrum shape of the reference oscillation wavelength (reference light 2) is divided into two. The present inventors have found that it changes or changes depending on conditions. Therefore, in the position calculation based on the normal peak position (enlarged view of the reference light 2: FIG. 14B) and the center of gravity position of the spectrum waveform, the lamp light source emission line using the above material has a spectrum shape depending on temperature, pressure, and composition. Since it changes slightly, it was sometimes difficult to obtain a constant and accurate value.
[0013]
The present invention has been made in view of such problems of the prior art, and the object thereof is F₂A wavelength detector that uses a bromine emission line with an emission line close to the wavelength of the laser as the reference light, and can detect the wavelength stably and accurately by using the absorption part of the reference light. An apparatus and a fluorine molecular laser device equipped with the device are provided.
[0014]
[Means for Solving the Problems]
The wavelength detection device of the present invention that achieves the above-mentioned object is the wavelength detection device that makes the light from the reference light source and the light from the light source to be detected incident, performs spectral spectroscopy,
A bromine discharge lamp with self-absorption is used as the reference light source, and the self-absorption line is used as a reference wavelength.
[0015]
In this case, the bromine discharge lamp is preferably sealed so that the Br atom concentration is in the range of 0.003 to 0.150 μmol / cc, and in particular, the Br atom concentration is sealed at 0.04 μmol / cc or more. It is preferable.
[0016]
Note that a fluorine molecular laser device is suitable as the light source to be detected.
[0017]
The present invention includes a fluorine molecular laser device including the above-described wavelength detection device.
[0018]
In that case, there are a fluorine molecular laser device that selects an emission wavelength based on wavelength data detected by the wavelength detection device, and a fluorine molecular laser device that stabilizes the emission wavelength.
[0019]
In these fluorine molecular laser devices, it is desirable to detect the wavelength of the oscillation laser light by using a line near the wavelength 157.484 nm and a line near 157.639 nm from the bromine discharge lamp as the reference light.
[0020]
In the present invention, a bromine discharge lamp with self-absorption is used as a reference light source, and the self-absorption line is used as a reference wavelength. Therefore, there is very little possibility that the self-absorption line is shifted. The fluorine molecular laser device equipped with the wavelength detection device can oscillate a predetermined wavelength stably and accurately over a long period of time, and is suitable for both refractive and catadioptric semiconductor exposure devices. It becomes a light source.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Before describing an embodiment of the wavelength detection device of the present invention and a fluorine molecular laser device using the same, first, a bromine discharge lamp as a reference light source used in the present invention will be described. The bromine discharge lamp is the same as that proposed in Japanese Patent Application No. 2000-345719.
[0022]
FIG. 2 is a diagram showing a configuration example of a bromine discharge lamp 10 as a reference light source for controlling the oscillation laser light of the fluorine molecular laser device. For example, the discharge vessel 1 having a length of about 150 mm and an outer diameter of about 20 mm is composed of a main body. It consists of a case 2 and a window member 3. The main body case 2 has a substantially cylindrical shape, and is made of, for example, borosilicate glass or quartz glass. The window member 3 is for taking out vacuum ultraviolet light generated inside the container, and is attached so that a substantially disk-shaped member made of synthetic quartz glass, magnesium fluoride, or lithium fluoride closes one end 2a of the main body case 2. . Two electrodes 4 a and 4 b made of, for example, copper or aluminum are wound around the outer surface of the main body case 2 in close contact with each other, and a connection line from the electrodes 4 a and 4 b is connected to the AC power source 5. Is done. The width of the electrodes 4a and 4b is, for example, 10 mm, the distance between the electrode 4a and the end of the discharge vessel 1 is, for example, 20 mm, and the distance between the electrode 4b and the window member 3 is, for example, 50 mm.
[0023]
Inside the discharge vessel 1 are enclosed bromine atoms as the luminescent component and argon as the starting buffer gas. Bromine atoms as the luminescent component can be enclosed in the range of 0.005 μmol / cc to 0.040 μmol / cc, more preferably in the range of 0.005 μmol / cc to 0.015 μmol / cc. On the other hand, the rare gas is at least one gas selected from xenon, argon, and krypton, and is in the range of 0.3 kPa to 3.5 kPa (normal temperature), more preferably 0.67 kPa to 2.67 kPa (normal temperature). ) Is enclosed in the range.
[0024]
In addition, the discharge vessel 1 does not require any substance other than bromine atoms as the luminescent material.
[0025]
From the discharge plasma 6 of such a bromine discharge lamp 10, as shown in FIG. 3, main fluorine molecules (F₂) Laser oscillation line λ₁= Light having an emission line of 157.639 nm and 157.5484 nm is emitted in the vicinity of 157.6299 nm. As described in Japanese Patent Application Laid-Open No. 2000-249600, one or two or more emission lines are used as reference light for wavelength detection of a fluorine molecular laser. In the case of a bromine discharge lamp, the wavelength of the fluorine molecular laser beam is detected using at least one of the emission lines of 157.639 nm and 157.584 nm.
[0026]
4 is an enlarged view of the vicinity of the 157.484 nm line of FIG. 3, and FIG. 5 is an enlarged view of the vicinity of the 157.639 nm line of FIG. 3 to 5, the amount of bromine (Br) atoms enclosed in the main body case of the bromine discharge lamp is 0.0005 μmol / cc, 0.0016 μmol / cc, 0.003 μmol / cc, 0.005 μmol / cc, The spectral characteristics of a bromine discharge lamp when changing to 0.03 μmol / cc are shown. Br atoms can be introduced into the lamp by several methods. For example, Br₂ Or enclosed as CH₂Br₂ Or in the form of hydrogen bromide (HBr). Further, argon (Ar) is sealed as a starting buffer gas at 3.3 kPa.
[0027]
The spectral characteristics shown in FIGS. 3 to 5 are measured by a spectrometer using a diffraction grating.
[0028]
As apparent from FIGS. 3 to 5, in the 157.484 nm line and the 157.639 nm line, as the Br atom concentration is higher, a dip (dent) portion due to self-absorption in the spectral distribution becomes more prominent.
[0029]
The Br atom concentration region where dip due to self-absorption does not occur is lower than the Br atom concentration region where dip occurs. Therefore, the intensity of light emitted from the lamp is weak due to the decrease in Br atom concentration, and further, when the Br atom concentration decreases due to lamp lighting, the light intensity becomes unstable, and when used as a reference light source for a wavelength detector, S / N ratio deteriorates and measurement accuracy deteriorates. Further, since the peak shape of the spectrum waveform becomes unstable, it is difficult to specify the peak position (channel) in the sensor of the wavelength detection device.
[0030]
The Br atom concentration region where dip due to self absorption occurs is higher than the Br atom concentration region where dip does not occur. Therefore, the intensity of light emitted from the lamp is strong due to the increase in Br atom concentration. It can be seen from FIG. 5 that when the Br atom concentration is decreased by lighting the lamp, the peak shape of the spectrum waveform changes, but the position of the valley bottom portion of the dip portion does not change. Therefore, when this self-absorption line is used as a reference line in the wavelength detection device, the wavelength position (channel) can be specified easily, stably, and with high accuracy. The intensity at the dip position was also large enough for measurement.
[0031]
In the bromine discharge lamp, the Stark expansion and Van der Waals expansion can be ignored. Therefore, it is considered that the deepest part of the dip caused by this self-absorption is very unlikely to shift. Therefore, when the dip portion is used as the reference line of the reference light source, the measurement accuracy of the wavelength detector is stably improved.
[0032]
In the 157.484 nm line shown in FIG. 4, dip due to self-absorption was observed when the Br atom concentration was 0.003 μmol / cc or more. In the 157.639 nm line shown in FIG. 5, dip due to self-absorption was observed when the Br atom concentration was higher than 0.003 μmol / cc. Therefore, when at least the Br atom concentration is greater than 0.003 μmol / cc, a dip due to self absorption is observed in the line near 157 nm of the Br discharge lamp. In particular, in the 157.639 nm line, a clear dip portion can be confirmed when the Br atom concentration is 0.03 μmol / cc.
[0033]
In FIG. 6, the amount of bromine (Br) atoms enclosed in the main body case of the bromine discharge lamp is changed to 0.030 μmol / cc, 0.050 μmol / cc, 0.150 μmol / cc, and 0.250 μmol / cc. Shows the spectral characteristics of the bromine discharge lamp. As apparent from FIG. 6, in the 157.484 nm line and the 157.639 nm line, when the Br atom concentration is 0.150 μmol / cc or more, the light intensity becomes substantially zero. That is, both lines are not released to the outside due to self-absorption.
[0034]
From the above, when the Br atom concentration is in the range of 0.0005 to 0.150 μmol / cc, dip due to self-absorption is observed in at least one of the lines near 157 nm of the bromine discharge lamp. In addition, within the range of 0.003 to 0.150 μmol / cc, dip due to self absorption is observed in both the 157.484 nm line and the 157.639 nm line.
[0035]
When the lamp is turned on, Br atoms in the main body case are consumed by reacting with the borosilicate glass in the main body case, and the number of Br atoms contributing to light emission is reduced. That is, as the lighting time elapses, the Br atom concentration gradually decreases. Therefore, it is desirable that the concentration of Br atoms enclosed in the lamp body is as high as possible from the viewpoint of the life of the lamp. However, when the concentration is close to 0.150 μmol / cc, the strength due to self-absorption becomes too small, which is not preferable.
[0036]
In the bromine discharge lamp proposed in Japanese Patent Application No. 2000-345719, from the viewpoint of practical lamp intensity, the Br atom concentration is preferably 0.005 to 0.04 μmol / cc as described above, and 0.04 μmol / cc. If it exceeds cc, the strength decreases due to self-absorption, which is undesirable.
[0037]
In the present invention, the focus is on the 157.484 nm line and the 157.639 nm line, and the focus is on positively using the dip due to self-absorption as the reference line in these lines. Thus, a range of Br atom concentration of 0.003 to 0.150 μmol / cc is effective. In particular, in order to set the lamp life so that dip due to self-absorption occurs for as long as possible even when consumption of Br occurs during lamp lighting, it is enclosed in the lamp body with a Br atom concentration as rich as possible. For example, it is desirable to seal 0.04 μmol / cc or more in the lamp body.
[0038]
As described above, the bromine discharge lamp used for the reference light source of the wavelength detection device of the present invention adjusts the Br atom concentration so that dip due to self absorption occurs, and uses the self absorption line as the wavelength reference. The S / N ratio is large, the reference position (channel) can be specified easily, and stable and highly accurate wavelength detection is possible.
[0039]
Next, an embodiment of the wavelength detection device of the present invention using such a self-absorption line of a bromine discharge lamp as a reference wavelength will be described.
[0040]
FIG. 1 is a schematic diagram of a wavelength detection device having one input port for each of a reference light source and a detected light source according to the present invention. In this wavelength detection device, a bromine discharge lamp 10 as shown in FIG. 2 is arranged in the reference light source unit 11 of the spectroscope 20, and the detected light guide unit 12 is supplied from, for example, a fluorine molecular laser device that is a detected light source. Introduce detected light. The reference light from the reference light source unit 11 enters the beam combiner 15 through the lens 14, and the detected light from the detected light guide unit 12 enters the beam combiner 15 through the diffuser 13 and the lens 14. . The reference light and the detected light synthesized by the beam synthesizer 15 pass through the entrance slit 21 of the spectroscope 20, sequentially through the collimating concave mirror 22, the diffraction grating 23 as a dispersive element, and the condensing concave mirror 24. Produces a wavelength-dispersed spectrum on the focal plane. A spectral array 26 such as a photodiode array (PDA) having a large number of discrete detection channels in the wavelength dispersion direction and a CCD is disposed on the surface, and a spectral waveform as shown in FIG. 7 is observed.
[0041]
In the example described above, the reference light and the detected light are combined and detected at the same time, but may be detected separately without combining them.
[0042]
The reference light 1 and the reference light 2 in FIG. 7 are lines of two wavelengths (157.4841 nm, 157.6387 nm) of the bromine discharge lamp 10 that is a reference light source, and the two lines are accurate on the horizontal axis. If the position is known, for example, as shown in Japanese Patent Laid-Open No. 2000-162047, the actual characteristic value of the spectroscope 20 is calculated, the detection positions of the reference light 1 and 2 and the detected light on the sensor 26, and the calculated spectral value. Based on the actual characteristic value of the spectrometer 20 and the known wavelengths of the reference lights 1 and 2 (157.4841 nm, 157.6387 nm), the characteristic of the spectrometer 20 is calculated using a calculation method for calculating the wavelength of the detected light. Even in the case of change, the wavelength of the light to be detected output from the fluorine molecular laser device that is the light source to be detected can be accurately detected without error.
[0043]
Here, when the bromine discharge lamp 10 as the reference light source has sufficient intensity as a wavelength reference of 157 nm, as described with reference to FIGS. 3 to 6, dip due to self-absorption is likely to occur, for example, 157.639 nm. In the line (reference light 2), a valley as schematically shown in FIG. 7 occurs. When the wavelength is specified using the reference lights 1 and 2, as described above, the self-absorption line is more stable than the light emission line. In particular, in the case of an absorption line of a bromine discharge lamp, since absorption occurs almost together with light emission as compared with an Hg lamp, once the absorption line is confirmed, the bottom position as the absorption position is stable.
[0044]
Actually, when a depression due to self-absorption well known in an Hg lamp or the like is generated in the waveform of the reference light 2, the waveform due to self-absorption is calculated by calculating the minimum value of the self-absorption portion as the measurement wavelength position of the light. Therefore, the wavelength can be calculated with high accuracy.
[0045]
In this case, a self-absorption position can be easily calculated by determining a reference light range to be searched and searching for a valley portion in the range. When obtaining this minimum position, as schematically shown in FIG. 8, the measurement value of the measurement point (discrete detection channel position of the sensor 26) can be used as the reference wavelength. By performing approximation such as three-point approximation, Lorentz approximation, spline approximation, etc. from the values of measurement points (X1, Y1) and (X3, Y3) on both sides including Y2), the minimum position between the channels (star in FIG. 8). The position of the mark) can be interpolated and determined, and more accurate wavelength measurement is possible. The dashed curve in FIG. 8 is a quadratic curve that passes through the measurement points (X1, Y1) and (X3, Y3) on both sides including the bottom position (X2, Y2) by three-point approximation, and the minimum point is the channel. It becomes the minimum position (star) between.
[0046]
Here, in the three-point approximation, the bottom position is determined as follows.
When Y1 = Y3 or Y1-2Y2 + Y3 = 0,
Bottom position: X2
Otherwise
Bottom position: X2 + (Y1-Y3) / [2 (Y1-2Y2 + Y3)]
It becomes.
[0047]
In the Lorentz approximation, the bottom position is determined as follows.
[0048]
Y = K × a²/ [(X-b)²+ A²]
In a function passing through three points (X1, Y1), (X2, Y2), (X3, Y3),
b = [X1²(Y1 * Y3-Y1 * Y2) + X2²(Y1 * Y2-Y2 * Y3) + X3²(Y2 * Y3-Y1 * Y3)] / {2 [X1 (Y1 * Y3-Y1 * Y2) + X2 (Y1 * Y2-Y2 * Y3) + X3 (Y2 * Y3-Y1 * Y3)]}
a²= [(X3-b)²Y3- (X2-b)²Y2] / (Y2-Y3)
K = [(X2-b)²+ A²] Y2 / a²
And the bottom position (Xp, Yp) is
Xp = b
Yp = K
It becomes.
[0049]
By the way, the reference light 1 (157.48441 nm) of the bromine discharge lamp 10 sometimes has a gentle waveform as a result of slight observation of peak self-absorption as schematically shown in FIG. 4). In the case of the waveform as shown in FIG. 9, since the minimum position of the depression often fluctuates around the measurement peak position, the bottom position fluctuates greatly in simple approximation. In order to prevent this, there are a method of taking the center of gravity and a method of taking the center value of the channels included in the peak FWHM within a certain range. Of course, not FWHM, 10% of peak value or 1 / e²For example, a method for obtaining the center value of the channels included in the above may be set according to the spectrum shape.
[0050]
Note that, when detecting a fluorine molecular laser oscillation line that is light to be detected, the peak is a steep peak, but if the peak position is determined only by the measurement point depending on the waveform or the accuracy of the spectroscopic device, the measurement error may increase. In this case, the peak detection position is calculated by three-point approximation or Lorentz approximation, the center of gravity of the spectrum is obtained, and the position is determined. As a result, the fluorine molecular laser oscillation line can be positioned with high accuracy, and the wavelength of the wavelength detection light can be calculated with higher accuracy using this.
[0051]
In the present invention, a detected fluorine molecular laser beam from a fluorine molecular laser device is introduced as a detected light source into the detected light guide section 12 of FIG. 1 and synthesized with the reference light from the bromine discharge lamp 10 by the beam combiner 15. Then, spectral spectroscopy is performed by the spectroscope 20 and a spectrum waveform is detected by the spectrum sensor 26, and the positions of the reference light 1 and 2 of the bromine discharge lamp 10 and the inspected light from the fluorine molecular laser on the spectrum sensor 26 are By accurately deriving by applying the above method, the absolute wavelength of the light to be inspected (fluorine molecular laser oscillation line) can be detected accurately using one or more reference light positions and the position of the light to be inspected. .
[0052]
Actual calculation results will be described. FIG. 10 shows a spectrum waveform obtained when a line-selected laser beam is detected. The reference light 1 is 157.48410 nm light from the bromine discharge lamp 10, and the reference light 2 is 157. The reference light 1 uses the channel at the center of the channel included in the half value of the peak intensity (FIG. 9), and the reference light 2 obtains the self-absorbing portion channel by three-point approximation (see FIG. 8). ). From these two sensor channels, the corresponding wavelength, and the peak channel (determined by three-point approximation) of the measured line-selected fluorine molecular laser oscillation line (detected light), the main of the fluorine molecular laser oscillation line A wavelength of 157.63157 nm was derived by calculation. The fluorine molecular laser oscillation line changes depending on the gas conditions.
[0053]
Next, an embodiment of a fluorine molecular laser device using the wavelength detector according to the present invention as shown in FIG. 1 will be described.
[0054]
FIG. 11 is a diagram showing a configuration example of a line select type fluorine molecular laser device used in a catadioptric exposure apparatus. As shown in FIG. 11, windows 33 and 34 are provided at both ends of the laser chamber 31. In the laser chamber 31, two discharge electrodes 32, that is, an anode electrode and a cathode electrode, are arranged vertically (in front of and behind the paper surface in parallel with the paper surface). A high voltage for discharge is applied between these electrodes 32 by a high voltage power source (not shown). The discharge direction is a vertical direction orthogonal to the paper surface. In the laser chamber 31 filled with a laser gas as a laser medium, a discharge is generated between the two electrodes 32 to excite the laser gas and cause laser oscillation. In FIG. 11, the laser resonator includes the following output coupler 36 and a total reflection mirror 113.
[0055]
A line select module 100 is disposed behind the laser chamber 31. The line select module 100 is, for example, CaF₂The angle dispersive element 115 and the total reflection mirror 113 including the prism 111 and the prism 112 are arranged in this order. The angle dispersion direction of the angle dispersion element 115 is a horizontal direction orthogonal to the discharge direction. A slit 35 and an output coupler 36 are arranged in this order on the front side of the laser chamber 31.
[0056]
The laser chamber 31 is filled with a gas such as a laser gas via a gas supply line 71 connected to the laser chamber 31 and a gas supply source (not shown). The gas supply line 72 is provided with a valve 73, whose opening and closing is controlled by the gas controller 70.
[0057]
The gas sealed in the laser chamber 31 is exhausted through a gas exhaust line 72 connected to the laser chamber 31 and a gas exhaust means such as a vacuum pump (not shown). The gas exhaust line 72 is provided with a valve 74, whose opening and closing is controlled by the gas controller 70.
[0058]
Wavelength λ, which is the stronger of the fluorine molecular laser device₁The line selection of the oscillation line (= 157.6299 nm) is performed as follows. Two main oscillation lines λ₁, Λ₂The laser beam including (= 157.5233 nm) has a different refraction angle in each of the oscillation lines due to the dispersion action of the angle dispersion element 115 including the prisms 111 and 112. The beam emitted from the angle dispersive element 115 passes through the windows 33 and 34 and reaches the slit 35 having an opening. Where the oscillation line λ₁Only passes through the opening of the slit 35 and the oscillation line λ₂By disposing the angle dispersive element 115 so that other lines including the light are shielded by the slit 35, the oscillation line λ₁Can be selected.
[0059]
The wavelength detector of the present invention has two main oscillation lines λ₁, Λ₂Can be detected, and is used during alignment of the angle dispersive element 115 for line selection. Specifically, the monitor module 50 corresponding to the wavelength detection device of the present invention detects the wavelength of the laser beam, and the data is sent to the controller 60. The controller 60 has a wavelength λ₁The first driver 61 or the second driver 62 is driven to adjust at least one posture angle of the prism 111, the prism 112, and the total reflection mirror 130 so that only the oscillation line (= 157.6299 nm) is output.
[0060]
When laser light is output for a long time, the laser light is absorbed in the prisms 111 and 112, the temperature of the prisms 111 and 112 rises, the refractive index of the prisms 111 and 112 increases, and the refraction angle of the beam increases. Change. In the case of a fluorine molecular laser device, the traveling direction of the laser beam itself is shifted, and the optical axis of the laser resonator formed by the total reflection mirror 113 and the output coupler 36 is shifted, so that the laser output is reduced. In the case of a fluorine molecular laser device, the wavelength of the laser light is around 157 nm and the VUV (vacuum ultraviolet) region. As described above, as a material of the prism that transmits light in this wavelength region, in practice, CaF₂There is only. F of shorter wavelength than KrF laser beam and ArF laser beam₂Laser beam is CaF₂Absorption is large, and exposure F₂Since the average output of the laser required for the laser device is as large as 40 W, the temperature of the prisms 111 and 112 is likely to increase.
[0061]
The wavelength detection device of the present invention has a wavelength λ even when laser light is output for a long time, the refractive index of the prism increases, and the refraction angle of the beam changes.₁(= 157.6299nm) other than the oscillation line is not output, and it is also used to control the output to be maximized.
[0062]
Specifically, as in the alignment, the monitor module 50 detects the wavelength of the laser beam and sends the data to the controller 60. The controller 60 has a wavelength λ₁The first driver 61 or the second driver 62 is driven so that the output other than the oscillation line (= 157.6299 nm) is not output and the output is maximized, and at least the prism 111, the prism 112, and the total reflection mirror 130 are driven. One posture angle is adjusted.
[0063]
On the other hand, when the laser beam is output for a long time, the laser gas temperature in the laser chamber rises due to the heat generated by the discharge performed between the electrodes 32, the laser gas pressure changes, the wavelength of the laser beam changes, and the desired wavelength Deviation from wavelength.
[0064]
The wavelength detection device of the present invention has a wavelength λ of the line-selected laser light even if the laser light is output for a long time and the laser gas pressure changes.₁Is also used to control the wavelength so that becomes a desired value.
[0065]
Specifically, the monitor module 50 determines the wavelength λ of the laser beam.₁And the data is sent to the controller 60. The controller 60 compares the detection data with a predetermined wavelength value stored in advance. Detected wavelength λ₁If the value of is less than a predetermined value, the controller 60 determines the wavelength λ₁Is controlled to increase the laser gas pressure in the laser chamber 31 so as to shift to the longer wavelength side. That is, the controller 60 instructs the gas controller 70 to increase the laser gas pressure in the laser chamber 31. Based on this command, the gas controller 70 opens the valve 73 of the gas supply line 71 to supply gas from the gas supply source into the laser chamber 31 to increase the gas pressure in the laser chamber 31.
[0066]
Conversely, the detected wavelength λ₁If the value of is greater than the predetermined value, the controller 60 determines that the wavelength λ₁Is controlled so as to reduce the laser gas pressure in the laser chamber 31 so as to shift to the short wavelength side. That is, the controller 60 instructs the gas controller 70 to reduce the laser gas pressure in the laser chamber 31. Based on this command, the gas controller 70 opens the valve 74 of the gas exhaust line 72 and exhausts a part of the laser gas in the laser chamber 31 by the gas exhaust means to lower the gas pressure in the laser chamber 31.
[0067]
Next, FIG. 12 shows a configuration example of a narrow-band fluorine molecular laser device. Narrow band F₂A configuration example of the laser device is a line select type F shown in FIG.₂In the configuration example of the laser device, a band narrowing module 120 is disposed instead of the line select module 100 disposed on the rear side of the laser chamber 31, and the other components are the same. The narrow-band module 120 includes, for example, an expansion optical system 125 including one or more prisms 121 and 122 (or right-angle prisms 121 and 122 in the configuration example of FIG. 12), and an echelle diffraction grating 123 in a Littrow arrangement. These are arranged in this order. The laser resonator includes a diffraction grating 123 and an output coupler 36 mounted on the narrowband module 120. Narrowing of the spectrum is realized by wavelength selection by the diffraction grating 123.
[0068]
As described above, when laser light is output for a long time, the laser light is absorbed in the prisms 121 and 122, the temperature of the prisms 121 and 122 rises, the refractive index of the prisms 121 and 122 increases, and the beam The refraction angle changes. That is, the incident angle of light to the diffraction grating 123 changes, and F₂The wavelength of the laser beam emitted from the laser device is shifted.
[0069]
The wavelength detection device of the present invention is used for controlling so that a wavelength shift does not occur even when a laser beam is output for a long time and the refractive index of the prism is increased and the refraction angle of the beam is changed.
[0070]
Specifically, the monitor module 50 detects the wavelength of the laser beam, and the data is sent to the controller 60. The controller 60 drives the driver 63 so that the wavelength of the laser beam becomes a predetermined wavelength, adjusts the attitude angle of the diffraction grating 123, controls the incident angle of light to the diffraction grating 123, and stabilizes the wavelength. Take control.
[0071]
Note that the wavelength stabilization system may be configured to control the attitude angle of any of the right-angle prisms 121 and 122.
[0072]
As mentioned above, although the wavelength detection apparatus of this invention and the fluorine molecular laser apparatus using the same have been demonstrated based on the principle and Example, this invention is not limited to these Examples, A various deformation | transformation is possible.
[0073]
According to the present invention, F₂Carbon C, iron Fe, sodium Na, fluorine F, magnesium Mg, aluminum Al, argon Ar, calcium Ca, scandium Sc, chromium Cr, manganese Mn having emission lines close to the wavelength of the laser and having a light intensity above a certain level Even in a wavelength detector that uses one or more emission lines of nickel Ni, copper Cu, germanium Ge, arsenic As, and platinum Pt as reference light, it is stable by using the self-absorption part of the reference light. Thus, it is estimated that an accurate wavelength can be detected.
[0074]
【The invention's effect】
As is clear from the above description, according to the wavelength detection device of the present invention and the fluorine molecular laser device using the same, a bromine discharge lamp with self-absorption is used as a reference light source, and the self-absorption line is used as a reference wavelength. Since the possibility of shifting the self-absorption line is extremely low, the wavelength detection accuracy is high and stable, and the fluorine molecular laser device equipped with the wavelength detection device is stable and accurate over a long period of time. It can oscillate, and is an exposure light source suitable for both refractive and catadioptric semiconductor exposure apparatuses.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of a wavelength detection apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of one embodiment of a bromine discharge lamp as a reference light source.
FIG. 3 is a diagram showing an example of emission spectral characteristics from a bromine discharge lamp.
4 is an enlarged view near the 157.484 nm line of FIG. 3;
FIG. 5 is an enlarged view of the vicinity of the 157.639 nm line of FIG. 3;
FIG. 6 is a diagram showing spectral characteristics when the amount of bromine atoms enclosed in a bromine discharge lamp is changed.
7 is a diagram showing an example of a spectrum waveform obtained with the arrangement of FIG. 1; FIG.
FIG. 8 is a diagram schematically showing an oscillation line for calculating a self-absorption position.
FIG. 9 is a diagram for explaining a peak position calculation method when there is little self-absorption of peaks.
FIG. 10 is a diagram showing a spectrum waveform actually obtained and a detection result based thereon.
FIG. 11 is a diagram illustrating a configuration example of a line select type fluorine molecular laser device according to the present invention.
FIG. 12 is a diagram showing a configuration example of a narrow-band fluorine molecular laser device according to the present invention.
FIG. 13 is a diagram for explaining two main oscillation wavelengths of the fluorine molecular laser device.
FIG. 14 is a diagram for explaining a spectrum shape of bromine having an emission line closest to the fluorine molecular laser device and problems in using it.
[Explanation of symbols]
1 ... Discharge vessel
2. Body case
2a ... One end of the body case
3. Window member
4a, 4b ... electrodes
5… AC power supply
6. Discharge plasma
10 ... Bromine discharge lamp
11 ... Reference light source
12 ... Detected light guide
13 ... Diffuser
14 ... Lens
15 ... Beam combiner
20 ... Spectroscope
21: Incident slit
22 ... Collimating concave mirror
23 ... Diffraction grating
24 ... Condensing concave mirror
26 ... Spectrum sensor
31 ... Laser chamber
32 ... Electrode
33, 34 ... Wind
35 ... Slit
36 ... Output coupler
50 ... Monitor module
60 ... Controller
61. First driver
62 ... Second driver
63 ... Driver
70 ... Gas controller
71 ... Gas supply line
72 ... Gas exhaust line
73, 74 ... Valve
100 ... Line select module
111, 112 ... Prism
113 ... Total reflection mirror
115. Angular dispersion element
120 ... Narrow band module
121, 122 ... Prism
123 ... Echelle diffraction grating
125 ... Magnifying optical system

Claims (8)

In the wavelength detection device that makes the light from the reference light source and the light from the light source to be detected incident, performs spectral spectroscopy, and detects the dispersed spectrum,
A wavelength detection apparatus using a bromine discharge lamp with self-absorption as the reference light source, and using the self-absorption line as a reference wavelength. 2. The wavelength detecting device according to claim 1, wherein the bromine discharge lamp is sealed so that a Br atom concentration is in a range of 0.003 to 0.150 [mu] mol / cc. The wavelength detection apparatus according to claim 2, wherein the bromine discharge lamp is filled with a Br atom concentration of 0.04 µmol / cc or more. 4. The wavelength detection device according to claim 1, wherein the light source to be detected is a fluorine molecular laser device. A fluorine molecular laser device comprising the wavelength detection device according to claim 1. 6. The fluorine molecular laser device according to claim 5, wherein an emission wavelength is selected based on wavelength data detected by the wavelength detection device. 6. The fluorine molecular laser device according to claim 5, wherein the emission wavelength is stabilized based on wavelength data detected by the wavelength detection device. 8. The wavelength of an oscillation laser beam is detected by using a line near a wavelength of 157.484 nm and a line near a wavelength of 157.639 nm from a bromine discharge lamp as reference light. The fluorine molecular laser device described.

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